(1) Field of the Invention
The present invention relates to a printed circuit board and amount structure thereof used in electronic apparatus (for example, various audio-visual apparatus, home electronic apparatus, communication apparatus, computer apparatus, and peripheral apparatus thereof) and others, as well as a method of producing these.
(2) Description of the Related Art
Conventionally, as a mount structure in an electronic apparatus, a mount structure in which an electronic component is mounted on a printed circuit board is used.
JP 2006-324642 A discloses a printed circuit board in which a through-hole is formed by performing a drilling treatment on a core substrate including a layer obtained by impregnating glass cloth with an insulating resin and solidifying it in a plate shape, and a through-hole via (through-hole conductor) made of Cu or the like is formed by the plating method or the like on the side wall of the through-hole.
Also, JP 2003-209359 A discloses a printed circuit board in which a through-hole is formed by a laser treatment in a core substrate made of an epoxy resin or the like and reinforced by glass cloth, and the inside of the through-hole is filled with an electrically conductive paste.
By the way, when the heat generated at the time of mounting or operating an electronic component is applied to the printed circuit board, a heat stress is liable to be generated between the glass cloth exposed to the inner wall of the through-hole and the through-hole conductor due to the difference in coefficient of thermal expansion between the glass cloth and the through-hole conductor. In particular, when a through-hole is formed in a core substrate by a drilling treatment, the surface of the glass cloth exposed to the inner wall of the through-hole is liable to be smooth, so that the through-hole conductor is liable to be exfoliated from the inner wall of the through-hole by the above-described heat stress.
Also, when a through-hole is formed in the core substrate by a drilling treatment, exfoliation between the glass cloth and the resin is liable to occur on the inner wall of the through-hole by mechanical stress or frictional heat. On the other hand, when a through-hole is formed in the core substrate by a laser treatment, exfoliation between the glass cloth and the resin is liable to occur on the inner wall of the through-hole by the heat of the laser.
In this manner, when exfoliation occurs between the glass cloth and the resin on the inner wall of the through-hole, there is a fear that, when a voltage is applied to the through-hole conductor, a part of the through-hole conductor that has been ionized by the voltage penetrates into the exfoliated site, whereby adjacent through-hole conductors may be short-circuited with each other. Further, when the through-hole conductor is exfoliated from the inner wall of the through-hole, disconnection may occur in the through-hole conductor. For this reason, electrical reliability of the printed circuit board is liable to decrease.